There is considerable evidence that a group of naturally occurring compounds, the polyamines, are present in high concentration in rapidly growing and dividing cells, including tumors. The major objective of this research project is to establish how the levels of these compounds are regulated and what function they play in the cell. This objective is being approached in bacterial cells through a study of mutants which require polyamines for optimal growth. The role of polyamines in animal cells is being studied in lymphocytes activated by concanavalin A, using an inhibitor of polyamine biosynthesis, methylglyoxal bis(guanylhydrazone).